The present invention relates to a method and network element for forwarding a multicast message received from an external packet data network, such as the Internet, to subscribers of a packet radio network, such as the General Packet Radio Service (GPRS) network.
The GPRS is a new GSM (Global System for Mobile Comnmunication) service that provides actual packet radio access for mobile GSM users. The main benefit of GPRS is that it reserves radio resources only when there is something to send. The same radio resource is shared by all mobile subscribers in a cell, providing effective use of the scarce resources. The need for packet radio is based on the high burstiness of data applications. GPRS facilitates a variety of applications, such as telemetry, train control systems, interactive data access, toll road charging systems, and Internet browsing using the World Wide Web.
When compared with the current circuit switched GSM network, the operation of GPRS is very different. The main objective of GPRS is to offer a connection to standard data network s using protocols such as TCP/IP (Transmission Control Protocol/Internet protocol), X.25, and CLNP (Connection Less Network Protocol).
In order to access the GPRS services, a mobile station (MS) first makes its presence known to a network by performing a GPRS attach. This operation establishes a logical link between the MS and a serving GPRS support node (SGSN), and makes the MS available for messages over GPRS, paging via SGSN, and notification of incoming GPRS data.
In order to transmit and receive GPRS data, the MS activates a desired packet data address. This operation makes the MS known in a corresponding gateway GPRS support node (GGSN), and interworking with external data networks can commence. User data is transferred transparently between the MS and the external data network with a method known as encapsulation and tunneling, wherein data packets are equipped with a GPRS-specific protocol information and transferred between the MS and the GGSN. This transparent transfer method lessens the requirement for a GPRS PLMN (Public Land Mobile Network) to interpret external data protocols, and it enables easy introduction of additional interworking protocols in the future. User data can be compressed and protected with retransmission protocols for efficiency and reliability.
The GPRS supports interworking with networks based on the Internet protocol (IP). The GSM PLMN GPRS service is an IP domain, and services offered to mobile terminals by a GSM service provider are globally addressable through the network operators addressing scheme.
However it has not yet been defined how an MS joins and leaves group calls received from an external packet data network (PDN), e.g. an IP/M group call received from the Internet, and how the GPRS network creates a connection between a multicast content provider and the MS.
It is therefore an object of the present invention to provide a method and network element for forwarding a multicast message, by means of which a mobile subscriber may join and leave a group call of an external packet data network.
This object is achieved by a method for forwarding a multicast message received from an external packet data network to subscribers of a packet radio network, comprising the steps of:
storing a subscriber-specific information, which defines multicast messages to be received by said subscribers, in a network element of the packet radio network;
establishing a point to point connection between a multicast content provider and a subscriber, when said subscriber-specific information indicates that the received multicast message is to be received by the subscriber; and
transmitting the multicast message from the multicast content provider to the subscriber via the established point to point connection.
Additionally, the above object is achieved by a network element for forwarding a multicast message received from an external packet data network to a subscriber of a packet radio network, comprising:
receiving means for receiving the multicast message from the external packet data network;
storing means for storing a subscriber-specific information which defines multicast messages to be received by the subscriber;
control means for establishing a point to point connection between a multicast content provider of a received multicast message and a subscriber, when the subscriber-specific information indicates that the received multicast message is to be received by the subscriber; and
transmitting means for transmitting the received multicast message to the subscriber via the established point to point connection.
Accordingly, a multicast service such as the IP-M service, of an external packet data network can be implemented in the packet radio network, i.e. the GPRS. Thus, the network element, for example, the GGSN, plays an IP-M arbitrator , role and acts as a distribution node in which subscriber-specific lists of multicast groups, for example IP-M groups, to which specific subscribers want to listen are stored. The multicast messages may then be forwarded to a respective subscriber using a usual point to point connection.
Hence, only minor changes of the respective network element in the packet radio network are required.
Preferably, a request for available groups for multicast messages may be transmitted from a subscriber to the network element, wherein an information defining the desired groups which the subscriber wishes to join is returned from the subscriber to the network element. The subscriber request may be transmitted with an IP-M context request.
Preferably, the subscriber-specific information is a list which maps group identities of multicast groups to connection identifications of subscribers belonging to the multicast groups. In particular, the group identity may be an IP-M group ID and the connection identification may be a GPRS tunnel ID.
The transmitting means of the network element may be arranged to transmit an information defining available multicast groups to subscribers which have indicated their interest in multicast messages. The multicast group information may be transmitted with an IP-M context procedure.